Quartz and glass are used not only as optical fiber materials, but also as high-reliability optical materials for optical communications. However, because of the high temperature treatment these materials require and the inferior productivity they offer, there is a need for organic materials for communication elements possessing better durability and processability. Polyimides, which are organic materials with the highest reliability, are widely used as raw materials for electronic components. On the other hand, organopolysiloxanes have been attracting attention in the field of optoelectronics due to their superior optical transmittance, electric insulation properties, optical stability, thermal stability, etc. The physical properties required of optical transmission materials, such as the absence of absorption in the communication wavelength band of 1300 nm to 1660 nm and the absence of birefringence due to polymer chain orientation, as well as heat resistance, moisture absorption resistance, and water resistance, which are regarded as very important properties for device assembly, are being constantly improved primarily with the aid of the above-mentioned polyimide and organopolysiloxane-based materials.
Although there are well-known polymeric optical materials, especially materials used for optical waveguides, obtained by adding a catalytic amount of an onium salt-based photoinitiator to an organopolysiloxane produced from an organochlorosilane (for example, phenyltrichlorosilane, methyltrichlorosilane) and a hydroxyl-containing epoxy compound (for example, glycidyl alcohol) as raw materials and irradiating the mixture with light (see Japanese Unexamined Patent Application Publication No. (hereinafter referred to as JP Kokai) Hei 9-124793), such materials suffer from problems associated with their insufficient adhesion to substrates and the fact that they are easily hydrolysable due to the bonding of epoxy-containing organic groups by Si—O—C linkages. Radiation (for example, UV)-curable compositions containing (A) a hydrolysable silane represented by the general formula RmSi (X)4 (where R is a non-hydrolysable organic group, X is a hydrolysable group, and m is between 0 and 3) or products of its condensation (for example, a product of co-hydrolysis and condensation of phenyltrimethoxysilane, methyltrimethoxysilane, and dimethyldimethoxysilane), (B) an organic onium salt-containing radiation (for example, UV)-curable composition producing acidic active substances by absorbing UV rays, and, furthermore, (C) a condensed aromatic compound (for example, anthracene, anthraquinone) are known (see JP Kokai 2003-185860), but the problem with this type of compositions is that they tend to contain air bubbles in cured films due to condensation based curing unless they are combined with defoaming agents.
On the other hand, there are known radiation (for example, UV)-curable silicone compositions comprising (a) an alkoxy- and epoxy-containing organopolysiloxane, (b) a cationic photoinitiator (for example, an onium salt), and (c) a free radical photoinitiator (for example, benzoin, acetophenone) or a sensitizer (for example, thioxanthone). In addition, there are known release coating radiation-curable silicone-containing compositions comprising (A) a liquid cationic polymerizable organopolysiloxane (epoxy-containing organopolysiloxane), (B) a cationic polymerization photoinitiator with an onium salt structure, and (C) a sensitizer (naphthalene derivatives, anthracene derivatives, and phenanthrene derivatives), both of which are used for imparting peelability and release properties against tacky substances, in particular by coating paper with such compositions and allowing them to cure. Alkoxy- and epoxy-containing methylpolysiloxanes (a) are considered preferable for use in the former compositions and in the latter compositions it is considered preferable that cationic polymerizable organopolysiloxanes should be linear or branched, with at least 85 mol % of silicon-bonded monovalent hydrocarbon groups represented by methyl groups; the problem with these compositions, however, is that their cured products have insufficient shape-retaining properties, solvent resistance, and optical transmittance in the communication wavelength band and exhibit considerable changes in the index of refraction and optical transmittance upon exposure to elevated temperatures.
Thus, as a result of in-depth investigations aimed at developing an active energy ray-curable organopolysiloxane resin composition free of such problems, the present inventors invented, and filed a patent application for, an active energy ray-curable organopolysiloxane resin composition that quickly cures upon irradiation with active energy rays (for example, UV rays) and contains no air bubbles in its cured product, with the cured product having superior resistance to hydrolysis, shape-retaining properties, and solvent resistance, providing a high optical transmittance in the communication wavelength band, and exhibiting insignificant changes in its refractive index and optical transmittance upon exposure to elevated temperatures (Japanese Patent Application No. 2003-412452). Incidentally, when such a composition is applied to a substrate (for example, a silicon substrate) and cured by irradiation with UV rays, the cured product exhibits insufficient adhesion to the substrate (for example, a silicon substrate) and can be easily peeled from the substrate after storage for approximately 3 months or ageing at about 100° C., which is a cause for concern about the stability of product quality. Attempts have been made to reduce residual stress in cured films, use special priming treatment, and treat the substrates with alkali in order to improve adhesion to the substrates with which compositions comes in contact in the process of curing, but sufficient effects have not been obtained.
The present invention was made by discovering that adhesion is improved if the composition is combined with a photo-sensitizer or photo-radical generator.